This disclosure relates generally to arc welding, and more specifically, to arc welding involving a shielding gas.
Welding is a process that has become ubiquitous in various industries for a variety of types of applications. For example, welding is often performed in applications such as shipbuilding, aircraft repair, construction, and so forth. Several welding techniques, such as Gas Metal Arc Welding (GMAW), Gas-shielded Flux Core Arc Welding (FCAW-G), and Gas Tungsten Arc Welding (GTAW), employ a shielding gas to provide a particular local atmosphere in and around the welding arc and the weld pool during welding. For example, commonly employed shielding gases include argon, carbon dioxide, helium, and oxygen. Shield gases and mixtures of shield gases may be selected to control, for example, arc stability, the formation of metal oxides, and the wettability of the metal surfaces.
For welding applications involving steel, one concern is the amount of diffusible hydrogen present in the weld during welding and after the welding process is complete. Hydrogen may be introduced into the weld from a number of sources, including moisture from the atmosphere, the metal surface, the welding electrode, or the shielding gas, and from oils, lubricants, or other coatings on the surface of the metal or welding wire during the welding operation. Hydrogen is readily soluble in steel exposed to high temperatures during the welding process; however, as the weld cools, the hydrogen may become increasingly insoluble in the steel and be rejected from solution. This may cause the hydrogen to collect at discontinuities and grain boundaries within the weld metal, resulting in localized regions of high pressure and strain within the weld. These regions of high pressure and strain can cause the weld to become brittle and crack, which may eventually lead to weld failure.
One method of limiting diffusible hydrogen in the weld is by preheating the metal, for example, to limit the amount of moisture present on the surface of the metal during the welding operation and/or provide better control of the metal microstructure by regulating the rate at which the metal cools. Such a preheat method may be common for situations involving the welding of thicker steel plates or high strength steels. However, fabricators can incur large costs (e.g., energy, equipment, time, etc.) associated with preheating steel to reduce the possibility of hydrogen cracking.